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  #21  
Old 21-07-2014, 03:34 PM
209herschel (Herschel)
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Thanks very much for all of the advice. I don't have tracking so I'm leaning toward as wide a field as I can afford. I'll look into the Meade ep now. I've got a 2x Barlow, bintell 2" ED. Would you all recommend something like a great 9mm ep that I could Barlow or would I get better results with a 6mm ep that isn't barlowed? Would a Barlow affect the quality of the view significantly? Thanks again.
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  #22  
Old 21-07-2014, 04:31 PM
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In that case the ES 82º 11mm and 8.8 barlow beautifully. The only problem is short ER, not as bad as a 9mm plossl though. I'm not a TV type but will say the TV barlows are the best. Your 2" GSO will be fine, I know I have one!
Can you borrow an ES to try it out?
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  #23  
Old 21-07-2014, 05:20 PM
209herschel (Herschel)
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In that case the ES 82º 11mm and 8.8 barlow beautifully. The only problem is short ER, not as bad as a 9mm plossl though. I'm not a TV type but will say the TV barlows are the best. Your 2" GSO will be fine, I know I have one!
Can you borrow an ES to try it out?
Thanks very much. The 8.8mm and 11mm get rave reviews everywhere also, even more so than the 6.7. If they barlow really well, I'm thinking the 11mm because 5.5 is pretty high, probably be about as good as I could possibly try in the yard.

I've only ever looked through my 9, 15 and 25mm GSO plossls! So my intention is to get to an event as soon as I can. I've kept my glasses on with the 15 and 25 and it wasn't too bad so I can't see how the ES pieces would be so bad. I also think I should be fine without glasses - I think it's really just a habit in that I never really take my glasses off. It's just so hard to go past the ES pieces, they seem such great value for money. Cheers
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  #24  
Old 21-07-2014, 05:32 PM
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I had the 11mm and 8.8mm ES82 eyepieces. The eye relief on the 11mm was particularly short, so I didn't keep it long.

I later sold the 8.8mm in favour of a Pentax XF 8.5mm, despite the narrower FOV.

You might want to consider the TMB planetary eyepieces. They go for around $60 used these days. Maybe get a 9mm and 6mm or 5mm to see how you like them. If they're not for you I'm sure you'll get your money back on resale.
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  #25  
Old 21-07-2014, 07:00 PM
bratislav (Bratislav)
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Originally Posted by 209herschel View Post
I have a 10" Dobsonian, f5.
Given that you have undriven telescope, there are two things you can do.

1. get a Paracorr. That will allow whatever eyepiece you get to work much more than approx 1 mm circle you get to play at f/5 before coma destroys the image. Between variable seeing and you nudging the scope all the time, chances of seeing planetary detail get to zero rather quickly. With Paracor, planet can drift from edge to edge and stay as sharp as it was in the middle. If you get a well corrected, wide angle design (I've seen Type 1 Nagler 4.7 go for as low as 100 bucks) you suddenly have many minutes to observe, not mere seconds at the time.

2. (better) Make a platform. Driven telescope will allow you to see much more on planets.

Contrary to popular belief, the eyepiece plays only a few last few percent in planetary work. That is, a high quality mirror on a driven mount with a cheap Chinese Plossl will work million times better than an average mirrored, undriven scope with a $$$$$ Zeiss Abbe Unobtanium polished by Norwegian virgins using Rouge made from rusting samurai swords during a total solar eclipse.
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  #26  
Old 22-07-2014, 07:18 AM
N1 (Mirko)
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Zeiss Abbe Unobtanium polished by Norwegian virgins using Rouge made from rusting samurai swords during a total solar eclipse.
Want!!!
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  #27  
Old 22-07-2014, 07:25 AM
209herschel (Herschel)
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There's a nice TMB 6mm planetary eyepiece for sale here

http://www.iceinspace.com.au/forum/s...d.php?t=123354
Hi there, I had a look at this one. I've tried checking the specs but I'm a little confused. There's a 9mm planetary II that's going in the classifieds for $45 but this 6mm was $100. Is there a difference or were there different series of the TMB Planetary II? I think I'll go with the 9mm. It has 12mm eye relief so I'll then know if the ES 6.7mm eye relief will be ok. It also has a 58 degree field so a bit better than my current 9mm plossl. I'll try to barlow it also to see what it looks like at 4.5mm.
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  #28  
Old 22-07-2014, 08:46 AM
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Originally Posted by bratislav View Post
Given that you have undriven telescope, there are two things you can do.

1. get a Paracorr. That will allow whatever eyepiece you get to work much more than approx 1 mm circle you get to play at f/5 before coma destroys the image. Between variable seeing and you nudging the scope all the time, chances of seeing planetary detail get to zero rather quickly. With Paracor, planet can drift from edge to edge and stay as sharp as it was in the middle. If you get a well corrected, wide angle design (I've seen Type 1 Nagler 4.7 go for as low as 100 bucks) you suddenly have many minutes to observe, not mere seconds at the time.

2. (better) Make a platform. Driven telescope will allow you to see much more on planets.

Contrary to popular belief, the eyepiece plays only a few last few percent in planetary work. That is, a high quality mirror on a driven mount with a cheap Chinese Plossl will work million times better than an average mirrored, undriven scope with a $$$$$ Zeiss Abbe Unobtanium polished by Norwegian virgins using Rouge made from rusting samurai swords during a total solar eclipse.
I would put driven platform first and foremost as a moving object is more difficult to concentrate on even if the entire field is sharp although the Paracorr option is a good idea.

With regards to your last sentence your limiting factor is your "average mirror". Put the good Zeiss eyepiece on a premium mirror and you will notice a difference.

Good eyepiece + good mirror = good view
Good eyepiece + bad mirror = bad view
Bad eyepiece + good mirror = bad view
Bad eyepiece + bad mirror = bad view

Your eye, local seeing, collimation and a few other factors also come into play.

Note I'm not saying all expensive eyepieces are good or all cheap eyepieces are bad. Just remember the eyepiece is half your telescope.
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  #29  
Old 22-07-2014, 09:28 AM
bratislav (Bratislav)
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Originally Posted by astro744 View Post

Good eyepiece + good mirror = good view
Good eyepiece + bad mirror = bad view
Bad eyepiece + good mirror = bad view
Bad eyepiece + bad mirror = bad view

Just remember the eyepiece is half your telescope.
Not even close. A cheap (not defective! just cheap) eyepiece will show you close to 99% (on axis) of what a "premium" one will, even in a perfect scope.
You will need a special subject (say, tiny low contrast details on Jupiter), once in a year seeing and lots of patience to see the difference between a ZAOII, AP superplanetary or TMB monocentric and an inexpensive no brand Ortho ("Tanny"). Been there, done that. Sold my "premium" set.

Read what people like Dragesco and Texereau have to say about it. Newsgroups and blogs are hardly a reference when it comes to optics.
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  #30  
Old 22-07-2014, 09:38 AM
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Originally Posted by bratislav View Post
Not even close. A cheap (not defective! just cheap) eyepiece will show you close to 99% (on axis) of what a "premium" one will, even in a perfect scope.
You will need a special subject (say, tiny low contrast details on Jupiter), once in a year seeing and lots of patience to see the difference between a ZAOII, AP superplanetary or TMB monocentric and an inexpensive no brand Ortho ("Tanny"). Been there, done that. Sold my "premium" set.

Read what people like Dragesco and Texereau have to say about it. Newsgroups and blogs are hardly a reference when it comes to optics.
Are you using a premium mirror or an average one? The view is only as good as the lowest common denominator.

Note I did not equate cheap with bad so my Boolean algebra still applies.
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  #31  
Old 22-07-2014, 05:16 PM
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I read below where you only have GSO eyepieces so far - I find them decent enough, but not wide enough for when pushing around a dob at higher power.

If you are going to get into going to dark sites and hunting faint galaxies, nothing beats a 2mm exit pupil. Just multiply the exit pupil you want by the f ratio, in your case 2mm x5= 10mm eyepiece. If you get a coma corrector that adjusts the f ratio, you'd get a different eyepiece result.

And, that 2mm exit pupil eyepiece should be as good and as wide an angle as you can afford. A 9mm eyepiece such as you have and were thinking of getting, will give a slightly smaller exit pupil. That makes it a bit harder to find galaxies out in the country, but gives slightly more pleasing views in light polluted skies.

Apply a good quality 2X Barlow, or even better a Powermate, to that 2mm exit pupil eyepiece, and you have a nice high powered view.
Regards,
Renato
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  #32  
Old 23-07-2014, 10:25 AM
bratislav (Bratislav)
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Originally Posted by astro744 View Post
The view is only as good as the lowest common denominator.

Note I did not equate cheap with bad so my Boolean algebra still applies.
Your "logic" implies that both objective and eyepiece contribute the same amount to image quality, which is very, VERY far from the reality.

Objective must deliver the wavefront with unbelievable precision; in case of a good planetary telescope, the maximum allowable wavefront error is in order of 1/10 wave (~1/20 on the optics). The eyepiece's task is to only magnify this image and deliver wavefront that is contained within eye's ability to resolve (which is several arc minutes). In case of planet observation, this condition has to be met only on axis (and near it).

Virtually ALL eyepiece designs that you can buy today will satisfy this condition. All of them. In other words, eyepiece tolerances are many thousands, if not millions of times more loose than those for objective side of the telescope. Good mirror or lens is made by a master optician and travels many many times from polishing machine to testing apparatus and back, often tested on the sky (star test) or interferometer before it is declared good enough. Eyepiece lenses are made in bulk by automated machines with no testing whatsoever of its optical surfaces (yes, even those at Zeiss and Leitz).

Have a look at on axis spot diagrams for eyepieces in Rutten and Van Venrooij's book (or more recent Smith, Ceragioili and Berry). All of them are virtually indistinguishable on axis. What you pay in a premium eyepiece is its off axis performance, first and foremost, and then we can talk about quality of polish and coatings. And those last two items make just about 1% or so of the total performance on planets.
Seeing differences in scatter (which will be the ONLY visible difference between your cherished Zeiss and my non brand Ortho on planets) is, as said before, not easy, and definitely not obvious. It requires special object, near perfect seeing and lots of patience; again, I have done this comparison, many times over the last 40-odd years. In refractors (yes, premium APOs as well as observatory class refractors like 24" and 20" Zeiss), reflectors (yes, premium reflectors with mirrors by LOMO, OMI, Suchthing, Zambuto, Galaxy, Lockwood, Barry Adcock, my own, and many others), catadioptrics (Maksutovs, SCTs, Wrights) and compound exotica (Schiefspieglers, Schupmanns) with same results.

Unless we talk about things like apparent field of view and off axis perfromance (which is totally irrelevant for planetary work), differences between eyepieces on axis are always going to be very, very small.

Last edited by bratislav; 23-07-2014 at 10:38 AM.
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  #33  
Old 23-07-2014, 10:56 AM
SkyWatch (Dean)
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Have you considered the Long Perng planetary eyepieces? I understand they are the same as the Orion "edge on", but only $79 at Andrews. I have used the 3mm and 5mm versions and they compare very well with a barlowed Nagler 13, and even my Nagler 3-6 zoom (which is magic by the way!). Not quite as wide-field (55-60 degree) as the Nagler 13, but nice and sharp across the field.
While on-axis performance is critical for any eyepiece, for a non-motorised dob it is good to have a relatively wide sharp field, even for planetary viewing, because it gives you more time looking and less pushing and waiting for the vibrations to settle again. It is really annoying if the image worsens significantly when the planet moves off centre, and this is often the case for budget eyepieces.
The LP's also have a 20mm eye-relief, which is very helpful with glasses and makes a big difference compared with plossls or orthos, irrespective of their cost.
All the best,
- Dean
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  #34  
Old 23-07-2014, 11:49 AM
bratislav (Bratislav)
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Originally Posted by SkyWatch View Post
While on-axis performance is critical for any eyepiece, for a non-motorised dob it is good to have a relatively wide sharp field, even for planetary viewing, because it gives you more time looking and less pushing and waiting for the vibrations to settle again. It is really annoying if the image worsens significantly when the planet moves off centre, and this is often the case for budget eyepieces.
Only if your telescope is capable of delivering sharp images over that wide field, which Newtonian cannot, due to coma.
A 10" f/5 Newt will deliver "planetary" quality wavefront (~1/10 wave, ~1/30 wRMS or ~0.95 Strehl) over a field that is only a tiny bit larger than 1mm.

The only way around that is if you add Paracorr. Or, better, an EQ platform.
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  #35  
Old 23-07-2014, 05:10 PM
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I suspect all this is getting quite confusing for the OP.

For the record, I have a 12" f5 scope, and the eyepieces I mentioned (even the cheap LP ones) are well corrected for coma at that f-ratio, and give sharp images across virtually the whole field, so you can watch a planet pretty much from one edge of the field to the other without having to move it into the centre of the field for the whole time.

For visual use they do a great job, and are a lot cheaper than a Paracorr or an equatorial platform...

- Dean
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  #36  
Old 24-07-2014, 05:32 AM
209herschel (Herschel)
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Originally Posted by SkyWatch View Post
Have you considered the Long Perng planetary eyepieces? I understand they are the same as the Orion "edge on", but only $79 at Andrews. I have used the 3mm and 5mm versions and they compare very well with a barlowed Nagler 13, and even my Nagler 3-6 zoom (which is magic by the way!). Not quite as wide-field (55-60 degree) as the Nagler 13, but nice and sharp across the field.
While on-axis performance is critical for any eyepiece, for a non-motorised dob it is good to have a relatively wide sharp field, even for planetary viewing, because it gives you more time looking and less pushing and waiting for the vibrations to settle again. It is really annoying if the image worsens significantly when the planet moves off centre, and this is often the case for budget eyepieces.
The LP's also have a 20mm eye-relief, which is very helpful with glasses and makes a big difference compared with plossls or orthos, irrespective of their cost.
All the best,
- Dean
Thanks very much Dean. I ended up buying a Tmb Planetary II 9mm to compare with my plossl. 58 degrees field and 12mm eye relief and they're supposed to be pretty good for planetary. I'd never even thought of the Long Perng and I knew Andrews had them. I'll start researching now - I appreciate the advice. The wide and sharp field on planetary is what I'm after before I get something great for dso which will be another topic entirely! Even with the 9mm plossl now, Saturn is pretty much through the field by the time the vibration settles and I've only seen it somewhat sharp when I've put the scope ahead and waited and had the focus on. Thanks again.
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  #37  
Old 24-07-2014, 10:30 AM
SkyWatch (Dean)
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Originally Posted by 209herschel View Post
Thanks very much Dean. I ended up buying a Tmb Planetary II 9mm to compare with my plossl. 58 degrees field and 12mm eye relief and they're supposed to be pretty good for planetary. I'd never even thought of the Long Perng and I knew Andrews had them. I'll start researching now - I appreciate the advice. The wide and sharp field on planetary is what I'm after before I get something great for dso which will be another topic entirely! Even with the 9mm plossl now, Saturn is pretty much through the field by the time the vibration settles and I've only seen it somewhat sharp when I've put the scope ahead and waited and had the focus on. Thanks again.
Regarding vibration: do you have vibration-isolation pads? I have found they cut the vibration time considerably and have been very useful. Meade and Orion make them, although a lot of people experiment with their own.
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  #38  
Old 24-07-2014, 11:48 AM
bratislav (Bratislav)
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For the record, I have a 12" f5 scope, and the eyepieces I mentioned (even the cheap LP ones) are well corrected for coma at that f-ratio, and give sharp images across virtually the whole field
Sorry to say, but I find that extremely unlikely. The only eyepieces that I know of that were capable of correcting Newtonian's coma are now long defunct Pretoria line.
Which makes sense, as any eyepiece with inbuilt negative coma would be completely unusable in refractors and SCTs. No manufacturer today would deliberately cut out such a significant slice of the market.

In any case, enjoy your eyepieces; that is what counts in the end - for all of us.

Last edited by bratislav; 24-07-2014 at 01:59 PM. Reason: spelling
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  #39  
Old 24-07-2014, 04:34 PM
209herschel (Herschel)
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Regarding vibration: do you have vibration-isolation pads? I have found they cut the vibration time considerably and have been very useful. Meade and Orion make them, although a lot of people experiment with their own.
Actually, I didn't even know there was any such thing. I'll look into that. Thanks again.
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  #40  
Old 26-07-2014, 07:22 AM
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I agree with Bratislav, except with these caveats:
If your scope is undriven and you are pushing it to follow a planet that drifts from side to side across the field, then definitely a coma corrector like the TeleVue Paracorr is called for. Otherwise, the image will be unsharp outside of a very small area in the center.
IF, on the other hand, you add a tracking platform and you now can hold the planets dead center, then, for planets, you don't need a coma corrector and just about any decent eyepiece will show you all the scope can see in the seeing conditions under which you're observing. Seeing is the greatest factor in determining the quality of the image, not the eyepiece. There is no magic eyepiece that suddenly makes seeing better.

For wider, extended, objects, then merely having tracking is not enough, and the coma corrector becomes more important again. We have all read innumerable accounts how such and such an eyepiece is "terrible in my dob", but "the images clean right up when a coma corrector is added". Well, duh. Of course they do--you just eliminated the coma from the mirror and, in the case of a Paracorr, also flattened the field slightly.

The primary difference you'd see between the top tier eyepieces like the Delos, and a lower-tiered one like the Hyperion, is at the edge of the field. Being free from induced astigmatism, the star images in the outer 50% of the field will be a lot better looking with the Delos. Will that matter for planets held in the center? Not really. Will it matter when you are letting the planet drift across the field? Yes. But we still get back to the coma corrector once again.

Where would I put my money if I were a hardcore planetary and lunar viewer?
1) tracking platform.
2) coma corrector
3) THEN maybe a better eyepiece, though it is hard to beat the lowly Plossl for planetary images.
so, maybe:
4) Gasoline. To drive me and my scope to sites where the seeing is better.
We have a few sites around here that are that much better than average. Everyone, with every eyepiece in every scope remarks that the images are better at those sites. Just points out how important seeing is.
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